For joining thermoplastic resin workpieces, an adhesion method using an adhesive agent and a welding method such as vibration welding, ultrasonic welding and laser welding, that melt resin to weld partially, are known.
The adhesion using the adhesive agent is avoided with regard to viewpoints of environment, safety and health, because of volatilization, diffusion and remainder of solvents.
The welding using vibration or ultrasonic is avoided with regard to viewpoints of quality and yield, because it is easy to transform or damage by exposing excess mechanical stress or overheating at wide area of the resin workpiece, and it is necessary to have to cut burrs at the welded position.
The laser welding is executed for example as follows. A laser-transmissible resin workpiece is piled onto a laser-absorptive resin workpiece. A laser beam is irradiated from above, and transmits through the transmissible resin workpiece. The laser beam reaches to the absorptive resin workpiece, and is absorbed into there, and causes the exothermic at limited area gently. Both resin workpieces melted by the laser beam thermally are joined.
The laser welding is satisfactory with regard to viewpoints of environment, safety and health because of no volatilization of solvents. And it is satisfactory to join the resin workpieces having complicated shape with sufficient strength by simple procedure at high yield without threat of exposing of stress or overheating.
Therefore, the laser welding is suitable to be executed in the manufacturing process of a precision instrument, electronic parts and a medical device that should avoid the thermal and vibratory influence to join the resin workpieces precisely.
In Japanese Patent Provisional Publication Nos. 9-510930 and 11-170371, the methods for laser welding of a laser-transmissible resin workpiece that is transparent, colorless, non-colored or black-colored, and a laser-absorptive resin workpiece that is opaque or black-colored are mentioned for instance.
According to the previous method of the laser welding of the transparent laser-transmissible resin workpiece and the laser-absorptive resin workpiece, the welded position has been visible unfortunately. Therefore usage has been practically limited.
According to the previous method of the laser welding of the laser-transmissible resin workpiece and the laser-absorptive resin workpiece having different color or same black respectively, the suitable hue and usage thereof have been limited.
If the laser welding of the previous white, clean and pretty resin workpieces including the white pigment such as zinc oxide is executed, it is inadequate for the strength thereof because the pigment is easy to reflect and disperse the laser beam, and does not make the laser beam transmit sufficiently.
The present invention has been developed to solve the foregoing problems.
It is an object of the present invention to provide especially a laser-transmissible resin composition exhibiting whitish hue of high whiteness degree. The composition is used as whitish base material for forming a workpiece that is capable of laser-transmission and the laser welding simply.
It is another object of the present invention to provide a method for the laser welding using it.